If the speakers do not appear to power on, the device's connection to the outlet or other power source may be the problem. Sometimes computer speakers emit a crackling sound caused by a faulty connection between the line-out plug on the back of the computer and the speakers.
Tech Advice offers a general computer speaker troubleshooting guide. Some common problems include no power to the speakers, one speaker powering on while the other does not, and white noise or other unwanted feedback. Popping sounds are another common problem with computer speakers; this can be fixed by purchasing a pack of ferrite beads that attach to your speaker wires and filter out unwanted noise.
Windows.Microsoft.com also offers a generalized computer speaker troubleshooting guide that addresses problems often encountered with computer speakers. One often overlooked solution to many speaker problems is adjusting the volume levels on your computer or other device. The problem may not lie within the speakers themselves, but rather may be occurring because your volume is set to mute or a level that is to low to hear. One final option to consider is that the speakers themselves may be broken beyond what is possible for a layman to repair. In this case, the solution is either to buy a new set of speakers or to bring the speakers to a repair shop. To test your speakers, unplug the speaker cable from the back of the computer, and insert the stereo plug into the headphone jack of your computer.